KVM: x86: Read guest RIP from within the kvm_nested_vmexit tracepoint

Use kvm_rip_read() to read the guest's RIP for the nested VM-Exit
tracepoint instead of having the caller pass in an argument.  Params
that are passed into a tracepoint are evaluated even if the tracepoint
is disabled, i.e. passing in RIP for VMX incurs a VMREAD and retpoline
to retrieve a value that may never be used, e.g. if the exit is due to a
hardware interrupt.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923201349.16097-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>